Abstract: Probiotics are live microorganisms that, when administered in sufficient amounts, may improve health. Often, probiotics are ingested as supplements in powder, pill or liquid forms, designed specifically for medicinal benefit. Yogurt can be an effective delivery vehicle for probiotics, but generally yogurts available in the United States are not formulated with attention to optimal probiotic strains or dose. Yogurt is also an attractive delivery agent because of its popularity with parents and children, likely improving compliance. We propose to evaluate yogurt formulated with a probiotic strain at a dose that results in recovery in stools. The long-term goal of this project is to demonstrate that a probiotic-containing yogurt beverage can be used successfully as a vehicle for delivering health-enhancing probiotics to children. The specific goals of this study are to determine if a yogurt drink containing Bifidobacterium lactis (Bb-12) at a minimum 1010 colony forming units (CFU)/per serving can prevent antibiotic-associated diarrhea (AAD). We have three specific aims to accomplish these goals. Aim #1: To determine if consumption of a yogurt drink containing a high dose of probiotics decreases the incidence of antibiotic-associated diarrhea in children ages 1-3 taking a penicillin-class antibiotic compared to a matching placebo drink. Aim #2: To evaluate the feasibility of children consuming a drinkable yogurt on a regular daily basis when the children are ill. Aim #3: To determine if the supplemental Bb-12 probiotics survive the gastrointestinal tract and can be recovered from the stools of participants consuming the Bb-12 yogurt drink. This proposal is in direct response to a PA and our Aims are in consort with NCCAM's mission. NCCAM has identified areas of research needing further investigation, stating, Use of adequately defined products and optimal dosage schedules in studies decreases the risk of failures that might discourage further research into otherwise promising modalities. Therefore, NCCAM recommends studies designed to: 1) determine active ingredients, pharmacology, bioavailability and optimal dosing; 2) identify surrogate markers; and, 3) assess study feasibility. The outcomes of these studies will form the basis for designing larger trials with an enhanced ability to detect a meaningful positive effect of the therapy under study. A readily available yogurt with high dose probiotics has the potential to positively impact the health of children around the world, as yogurt will likely be more appealing to both children and their parents for long term consumption than pharmaceutical-like probiotic preparations.